This has previously been solved by means of a device with a light source whose light beam has been angled by means of a rotating prism or mirror, which rotates 360° so that the rotating beam describes a plane of propagation around the device.
A problem with these known devices is that they require very accurate manufacturing so that the rotating parts do not angle the light beam incorrectly during the rotation. Additionally, at least one motor is needed to rotate them.
Another problem is that they are provided within four windows, which lead to four corner pillars for the holding of the windows, which blocks the propagation of the light plane. An attempt to get away from the problem with rotating parts and motors has been done in U.S. Pat. No. 3,820,903. In that the rotating parts have been replaced by a conical, reflecting prism which deflects a laser beam 90° so that a plane is formed 360° around the prism.
A problem connected with the use of a reflecting cone is that the device becomes very sensitive to angle deviations of the cone relative the incoming light beam since a small angle deviation there is enlarged in the plane of propagation, see FIG. 1b. The angle error will be doubled according to the law of reflection. A small angle error may at long distance give large position errors.